A human heart includes four heart valves that determine the pathway of blood flow through the heart: the mitral valve, the tricuspid valve, the aortic valve, and the pulmonary valve. The mitral and tricuspid valves are atrioventricular valves, which are between the atria and the ventricles, while the aortic and pulmonary valves are semilunar valves, which are in the arteries leaving the heart. Ideally, native leaflets of a heart valve move apart from each other when the valve is in an open position, and meet or “coapt” when the valve is in a closed position. Problems that may develop with valves include stenosis in which a valve does not open properly, and/or insufficiency or regurgitation in which a valve does not close properly. Stenosis and insufficiency may occur concomitantly in the same valve. The effects of valvular dysfunction vary, with regurgitation or backflow typically having relatively severe physiological consequences to the patient.
Recently, prosthetic valves supported by stent structures that can be delivered percutaneously using a catheter-based delivery system have been developed for heart and venous valve replacement. These prosthetic valves may include either self-expanding or balloon-expandable stent structures with valve leaflets attached to the interior of the stent structure. The prosthetic valve can be reduced in diameter, by crimping onto a balloon catheter or by being contained within a sheath component of a delivery catheter, and advanced through the venous or arterial vasculature. Once the prosthetic valve is positioned at the treatment site, for instance within an incompetent native valve, the stent structure may be expanded to hold the prosthetic valve firmly in place. One example of a stented prosthetic valve is disclosed in U.S. Pat. No. 5,957,949 to Leonhardt et al., which is incorporated by reference herein in its entirety.
Although transcatheter delivery methods may provide safer and less invasive methods for replacing a defective native heart valve, preventing leakage between the implanted prosthetic valve and the surrounding native tissue remains a challenge. Leakage sometimes occurs due to the fact that minimally invasive and percutaneous replacement of cardiac valves typically does not involve actual physical removal of the diseased or injured heart valve. Rather, the replacement stented prosthetic valve is delivered in a compressed condition to the valve site and expanded to its operational state within the diseased heart valve, which may not allow complete conformance of the stent frame within the native heart valve and can be a source of paravalvular leakage (PVL). As well PVL may occur after a heart valve prosthesis is implanted due to movement and/or migration of the prosthesis that can occur during the cardiac cycle. Movement due to changes in chordal tensioning during the cardiac cycle may be particularly problematic for mitral valve prosthesis, as chordal tensioning can axially unseat, lift or rock the prosthesis within or into the atrium resulting in PVL. Accordingly, there is a continued need to provide mitral valve prosthesis having structure that maintains sealing within the native anatomy during the cardiac cycle.